The present invention relates to a system for use in a photographic device such as a camera for calculating a light information value such as an f/stop number or shutter speed relative to a number of pieces of independent light information involved in taking one photograph.
When taking a photograph with a plurality of light sources such as strobes, it is necessary to calculate an optimum f/stop number for the total brightness resulting from the strobes being fired at the same time for taking one photograph. For this purpose, in a conventional system, the strobes are successively fired for measuring, at first, the light value (brightness times flashing time) of an object to be photographed from the lighting of each strobe, and then, the total light value is calculated by the use of a known system which is a so-called additive system of photographic exposure, being abbreviated as the APEX system. This total light value is used for further calculating through the APEX system the optimum f/stop number for a photograph to be taken with a plurality of strobes actuated at substantially the same time. A similar calculation stop has been necessary for taking a multiple exposure photograph.
Conventionally, a device for calculating the optimum exposure value on the basis of the above described system has employed a capacitor which accumulates an electric charge corresponding to the light value as the plurality of strobes are lighted sequentially.
However, the device and system of the above described type has disadvantages such as that the capacitance of the capacitor must be quite large for preventing the capacitor from being saturated at a rather low charge, thus, so that a large size capacitor is required. Furthermore, a capacitor with a large capacitance is not appropriate for precise measurement, since the degree of change in the charged voltage is very small for small light values. Therefore, the preciseness of the light measurement is reduced. In addition, where the time interval between the times of lighting of the strobes is quite long, the charge on the capacitor may leak off more or less during said time interval, resulting in a failure to obtain a precise calculation.
Accordingly, it is an important object of the present invention to provide a system which precisely calculates the exposure value without any failure.
It is also an important object of the present invention to provide a device which operates according to the system of the above described type.